Transitions of function and shape are key aspects of alveolar epithelial cell function during normal development as well as normal and abnormal interstitial remodeling. A major difficulty has been in defining methods and strategies for examining these transitions as they occur in vivo and in vitro. These transitions involve substantial changes in cell architecture which either lead to or are accompanied by changes in cell function such as surfactant production. We have targeted the cytoskeleton in our efforts to develop methods for studying alveolar epithelial cell structure-function relationships. We have, in particular, developed a unique panel of monoclonal antibodies against subclasses of the epithelial cell keratin intermediate filament proteins that appear to define epithelial cell transitions in the bleomycin model of fibrosis. Thus, we hypothesize that cytoskeletal protein undergo a change in isoform and organization as part of the process of changing shape and function. We plan to use these tools to study epithelial cell transitions during: 1) normal lung development; 2) during adult lung remodeling following pneumonectomy; 3) in two models of lung injury that appear to affect epithelial cells differentially, hyperoxia and bleomycin treatment; and 4) alveolar type II cells in culture. Our study will emphasize analysis of patterns of keratin antibody immunostaining at the light and electron microscope level. Parallel studies involving immunostaining and analyses of surfactant production will be carried out when the model and questions are appropriate. Studies of cells in culture or in specific substrate or matrix will be targeted at defining the relationship between epithelial cell shape and differentiated function. These experiments will answer fundamental questions regarding the nature of epithelial cell transitions in normal and pathologic tissue remodeling, as well as the relationship between shape and differentiated function of these cells.